Mortality Compression and Longevity Limits

pEOpLE ARE Living MuCH LOngER nOW. The life expectancies
of u.S. males and females, for example, increased more than 20 years
in the 20th century—from less than 50 years old in 1900 to more than
70 at the end of the century (Figure 1). This increase of approximately
30 years over the past 100 years comes out to about 0.3 year annually.

But it’s not just the United States.
According to the United Nations, life
expectancy worldwide had an average
increment of 0.25 year annually during
the second half of the 20th century. A
recent BBC report even predicted that
about one in five citizens of the United
Kingdom will live beyond age 100.

This prolongation of life is changingsocietal structures in both developed anddeveloping countries. In many of thesecountries, the number of elderly soonwill surpass the number of children aged5 and younger. This is not just becauseof increasing life expectancy but also be-cause of declining fertility rates. In theUnited States, 12 percent of the popula-tion was elderly in 2004—a proportionthat is projected to increase to 21 percentby 2050. Life expectancy in Taiwan andthe United States is about the same, butbecause of much lower fertility rates,Taiwan’s proportion of elderly in 2050( 37. 9 percent) will eclipse that of theUnited States.

But while there is no consensus about
future life expectancy, mortality rates
do share some common features. Rec–
tangularization of the survival curve, or
mortality compression, is one of them.

According to James Fries, a medical
doctor who wrote about mortality compression in a 1980 article published in
the New England Journal of Medicine,
this is a method in which mortality from
exogenous causes is eliminated—leaving
genetic factors as the primary cause for
the remaining variability in the age at
death. Figure 2 shows the survival curves
of Taiwanese females, in which the
mortality rates for infants and children
dropped significantly over the course
of 100 years. The majority of deaths occur between ages 65 and 85, accounting
for about 50 percent of deaths in 2000.
Following Fries’, concept of mortality
compression, the burden of lifetime illness is compressed into a shorter period
before death.

Some researchers have used rec–
tangularization to determine if human
life span has an upper limit. In research
published in 2000, Väinö Kannisto of
Germany’s Max Planck Institute for

a rectangular Survival curve Because of the rapid increase in life ex- pectancy over a relatively short period of time, there aren’t enough data to model elderly mortality rates.